Mr Brough has previously admitted to encouraging Mr Ashby, to make copies of the former Speaker's diary.

These were then leaked to the media in a bid to damage Mr Slipper.

"The Special Minister of State is in charge of government integrity. I think that it's not just a matter of whether or not Mal Brough should stand aside, which he probably should, it's now becoming a matter of Malcolm Turnbull's judgment on why he won't act," Mr Shorten said on Thursday.

Mr Brough has repeatedly refused to step aside.

Mr Ashby claimed Mr Slipper sexually harassed him but his case was tossed out of the federal court.

Justice Rares said it was politically motivated, blaming Mr Brough.

On Wednesday, Mr Palmer revived his claims in Parliament that Mr Brough has asked him in 2012 to fund Mr Ashby's case against Mr Slipper, possibly up to the tune of $200,000.